g2401_2500.s2484_count_palindromic_subsequences

Class Solution

java.lang.Object

g2401_2500.s2484_count_palindromic_subsequences.Solution

public class Solution
extends Object

2484 - Count Palindromic Subsequences.

Hard

Given a string of digits s, return the number of palindromic subsequences of s having length 5. Since the answer may be very large, return it modulo 109 + 7.

Note:

• A string is palindromic if it reads the same forward and backward.
• A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.

Example 1:

Input: s = “103301”

Output: 2

Explanation: There are 6 possible subsequences of length 5: “10330”,“10331”,“10301”,“10301”,“13301”,“03301”. Two of them (both equal to “10301”) are palindromic.

Example 2:

Input: s = “0000000”

Output: 21

Explanation: All 21 subsequences are “00000”, which is palindromic.

Example 3:

Input: s = “9999900000”

Output: 2

Explanation: The only two palindromic subsequences are “99999” and “00000”.

Constraints:

• 1 <= s.length <= 104
• s consists of digits.

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	countPalindromes(String s)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

countPalindromes

public int countPalindromes(String s)